First-principles study on elastic properties of Cu, (Cu ₁− x ,Ni x ) ₃ Sn and interfacial mechanical properties of (Cu ₁− x ,Ni x ) ₃ Sn/Cu in the lead-free solder joint

In this study, the elastic properties of Cu and (Cu x Ni 1− x ) 3 Sn were calculated to reveal the effects of Ni alloying on the interfacial mechanical properties of (Cu x Ni 1− x ) 3 Sn/Cu in lead-free solder joints. The results reveal that, within the thermodynamically stable domain of (Cu x Ni 1− x ) 3 Sn, the increase of Ni content can enhance the interfacial mechanical properties of (Cu x Ni 1− x ) 3 Sn/Cu, and increase the reliability of the lead-free solder joints. The enhancement mechanism can be attributed to the simultaneous improvements of oriented Young’s modulus and ductility of (Cu x Ni 1− x ) 3 Sn, achieved by Ni alloying. But higher Ni content beyond the thermodynamically stable domain of (Cu x Ni 1− x ) 3 Sn will deteriorate the interfacial mechanical properties by mechanical or thermodynamic mechanisms and decrease the reliability of the lead-free solder joints. The results presented in this study will not only unveil the effects of Ni alloying on the interfacial properties of lead-free solder joints, but also will provide a guidance for high-performance lead-free solder design by alloying strategies to meet the requirements for electronic device miniaturization and harsh environmental applications.